1. Field of the Invention
The present invention relates to a drilling tool, and in particular, to a drilling tool suitable for drilling process in which powdery and fine chips are generated at drilling.
2. Description of the Related Art
In recent years, composite materials such as glass fiber reinforced plastics (GFRP) or carbon fiber reinforced plastics (CFRP) have been in the spot light as materials having light weight and high strength. Composite materials have been used in various fields such as motor cycles, automobiles, railways, construction industries and medical care, including aerospace industries.
When performing cutting work in which such a composite material is used as a work piece, harmful powder dusts containing glass fibers, carbon fibers or the like are possibly generated due to the cutting. Therefore, an improvement in an operational environment is demanded.
On the other hand, there is known a concrete boring drill equipped with a dust suction hole for concrete powder dust suction extending through a drill body in an axial line thereof. A concrete boring drill described in Japanese Patent Laid-Open No. H09-272118(1997) is provided with a drill body and a tip which is embedded and fixed in a front end of the body on a diameter line to be arranged in such a manner that a front end portion and both side portions of the tip protrude from the body. The tip is formed in a flat-plate shape and an outer periphery at one end side of the flat surface is formed in a mountain shape. A dust suction hole extending through the body in the axial line is branched in a Y-letter shape at the front end portion to both sides of the tip, and both the branch ends are opened to be in positions substantially equal to rear edges of both the side portions or closer to the front end than the rear edges in a plan view of the tip.
However, in the drill disclosed in Japanese Patent Laid-Open No. H09-272118(1997), the dust suction hole is opened at a position away from the front end portion of the chip toward the side portion rear edge of the tip. Therefore, in cutting work generating powdery chips, chips generated by a cutting edge located at the front end portion of the tip possibly scatter without being sucked. Since the dust suction hole has an equal diameter until the front end portion thereof, a suction force gets the weaker as an opening of the dust suction hole is away from suction means, and therefore, the suction performance is not sufficient.
The present invention is made in view of the foregoing problems, and an object of the present invention is to provide a drilling tool which can restrict scattering of chips even in a case of performing cutting work in which powdery and fine chips are generated.